1. Field of the Invention
This invention relates to a method of prospecting for fish in lakes and oceans, and more particularly, but not by way of limitation, to water differential temperature measurement method for use in conjunction with boats for the express purpose of locating suitable or likely environments for specific varieties of fish.
2. Description of the Prior Art
In recent years it has been established that most species of fish, and perhaps all, have preferred temperature habitats and further need to seek temperatures within a certain tolerance range. The fish will, therefore, seek these preferred temperature areas in lakes and oceans if they can be found and will usually stay in those regions where the preferred temperatures prevail. If adequate food cannot be found in regions of preferred temperature, the fish will temporarily leave to feed and will thereafter return to this most desired habitat.
The temperature of the water in a lake, and within the stratifications of lakes, is often also closely related to the oxygen content of the water. Or to be more precise, we should say that the oxygen content of the water is closely correlated with the temperature of the water. For example, the surface temperature of many lakes gets quite warm during the summer, 80.degree. F. and above, and the oxygen is "boiled out" of the water so to speak, and for this reason many fish avoid such surface layers as much as they do on account of the direct effects of temperature. Oxygen solubility in water is a rather complicated function of temperature.
Recently, electrically operated thermometers have been available whereby fishermen can lower a temperature sensitive probe into the water by means of an electrical conducting cable and detect the temperature at a chosen depth. While the use of these instruments in the hand of expert fishermen greatly improves fishing catches, it is time consuming and most fishermen prefer the more familiar operations of fishing to those of finding the fish and recording temperatures. Fishing thermometers today generally employ a thermistor disposed in a probe at one end of an extremely long two-conductor cable, the other extremity of the cables being connected into one arm of a rather insensitive wheatstone bridge measuring circuit. Power is normally supplied by a single cell 1.5 volt battery connected across the wheatstone bridge terminals. The indicator of the typical fish thermometer is simply an ammeter which is connected across the arms of the said wheatstone bridge and provides a direct temperature readout based on the value of the standard resistor placed in the opposite arm of the wheatstone circuit.